Please refer to FIG. 1, in which a cross-sectional view of a water pump 1 commonly used in a water cooling heat-dissipating system of a conventional integrated circuit chip is schematically illustrated. As shown, the impeller 10 rotates clockwise to drive water inside the chamber of the water pump to flow along an arrow 19.
Further referring to FIG. 2A and FIG. 2B, the top structure and the bottom structure of the impeller 10 are schematically shown. As shown, a plurality of protruding blades 100 are arranged atop for driving the flow of the water cooling liquid. A plurality of through holes 11 are provided, penetrating the top face and the bottom face of the impeller 10, for the flow of the water cooling liquid into a channel space at the bottom of the impeller 10. While the water pump 1 is working, the water cooling liquid is thrown out due to a centrifugal force. Therefore, the water cooling liquid existing in the bottom space of the impeller 10 would be gradually decreasing. When the amount of the water cooling liquid inside the bottom chamber of the impeller 10 decreases to be less than a certain level, the pressure at the top and the bottom of the impeller 10 would become uneven, and the impeller 10 might deflect or unstable while rotating. As a result, the frictional force between the shaft 12 and the bearing 13 of the impeller would undesirably increase. Moreover, the presence of the through holes 11 of a relatively large diameter is also a factor resulting in liquid loss. The unsmooth rotation might result in unstable rotation speed and cause damages of the impeller, and further adversely affect the lift span of the water pump.